1. Field of the Invention
The present invention relates to ink-jet printers and more particularly to a cap system in such a printer which includes a rounded vent in which capillary action acts to reduce the potential for vent clogging.
2. Description of the Related Art
An ink-jet printer includes a replaceable printing cartridge having a printhead formed thereon. The cartridge includes a reservoir of ink which is fired through nozzles in the printhead onto a printing medium such as paper. The structure and operation of such printing cartridges is well known to those skilled in the art.
There are two primary constraints for maintaining ink-jet printheads when they are not in use. First, a sealed environment must be provided for the nozzles to prevent them from drying. Secondly, pressure variations between the sealed environment and the ambient pressure must be minimized. A relative pressure decrease in the sealed environment can cause priming of the nozzles, which in a three chamber pin may result in color mixing. A pressure increase can deprime the nozzles which can render them inoperable.
Prior ink-jet printers include a service station at one end of the travel path of a printing carriage upon which the printing cartridge is mounted. The service station includes a wiper for wiping the printhead to remove contaminants, dried ink and the like from the printhead surface containing the nozzle openings. Also provided is a cap which covers the printhead to prevent the ink in the nozzles from drying. The printer may be programmed to fire ink from the nozzles into the cap to create ink vapor within the cap to reduce drying of ink in the printhead nozzles. Such firing also clears the nozzles of any viscous ink.
Prior art printhead caps for ink-jet printers include vents to prevent a pressure differential across the nozzles. In an unvented cap a pressure spike may occur as the cap moves into and out of sealing engagement with the printhead. This reduces the magnitude of the spike, but also allows vapor to diffuse from the cap thereby increasing ink drying in the nozzles.
Ink drying in the nozzles is proportional to the rate of vapor diffusion from the cap. The rate of vapor diffusion is proportional to the cross-sectional area over which diffusion can occur divided by the length of the diffusion path. In order to minimize vapor diffusion it is therefore desirable to minimize the cross-sectional area of the vent while maximizing its length.
In addition to equalizing pressure, prior art vents also serve as a flow path to drain ink which collects in the cap therefrom. Prior art vents can clog with ink and thus cause undesirable pressure differentials across the nozzles. On the other hand, when the vent is made sufficiently large to prevent clogging, the vent is not a sufficiently effective vapor barrier to prevent drying of the ink in the printhead nozzles.
One prior art cap vent is disclosed in U.S. Pat. No. 5,027,134 issued Jun. 25, 1991 and assigned to the assignee of the present application. The disclosed vent has a square cross section and includes a space between the top surface of the vent and each sidewall. The ostensible purpose of the space is to wick ink from the vent by capillary action. This vent is disadvantageous for several reasons. Ink tends to collect in the lower corners of the vent where there is no space into which the ink can drain. Because the space is at the upper level of the vent, it has to fill with ink before the ink can flow into the space. This leads to clogging of the vent with ink. This vent is also very short, to reduce clogging, which renders it less effective as a vapor barrier than if a longer vent could be used.
It would be desirable to provide a cap system for an ink-jet printer which functioned as a highly effective vapor diffusion barrier without vent clogging.